In the food sector products are increasingly sought and offered, which the consumer can himself put into a ready-to-eat condition merely by heating in a baking oven or in a microwave oven. In that case the products are either already substantially completely in a finished cooked condition and are only heated for consumption or the products are still raw or only pre-cooked or pre-baked and are then further cooked or baked by the consumer to put them into the ready-to-eat condition.
Baking in a conventional baking oven is based on a combination of convection and radiant heat. The foodstuffs are heated from the surface inwardly so that the outside of the foodstuff receives more heat than the interior thereof, whereby it is possible to achieve a crispy exterior.
Heating in a microwave oven in comparison with heating in a baking oven affords a particularly convenient, simple, quick and energy-efficient method of thawing, heating, cooking and/or baking products. In that case the microwave radiation produces in the product dipole and molecular oscillations in the water molecules but also in other polar molecules, whereby heat is generated. In that case the heating effect is not based on the absorption of the microwave radiation at a given resonance frequency. Rather the water molecules constantly seek to become oriented in accordance with the alternating electromagnetic field of the microwave radiation, wherein the heat is produced as a dielectric loss in the entire foodstuff. Unlike the situation when heating in a conventional baking oven where the conduction of heat is from the surface of the product inwardly irradiation with microwaves involves heating substantially through the entire foodstuff at the same time, wherein the extent or the speed of heating at the centre of the foodstuff, in comparison with the heating effect at the surface of the foodstuff, can be very different or very similar depending on the respective depth of penetration of the microwave radiation. The depth of penetration of the microwave radiation is influenced inter alia by the water content and the temperature of the foodstuff. Intensity of microwave radiation decreases exponentially for example in water with an increasing depth of penetration. At any event, substantially no crust formation or surface browning of the foodstuff occurs by virtue of the penetration of the microwave rays through the foodstuff, which under most conditions is good. Particularly in the case of frozen foodstuffs microwave heating in the interior of the foodstuff is delayed to a greater or lesser degree, which is to be attributed to the usually high water or ice content.
The method of microwave heating is therefore not suitable for all kinds of foodstuffs, particularly when pronounced surface heating is wanted. For example dough items like bread, rolls or pizza, upon being heated in a microwave oven, generally become rather soft and moist and do not have any crust formation or browning of the outside of the product as the microwave radiation simultaneously heats the entire product and the necessary external heat which in the case of the radiant heat or convection heat generated in a baking oven, changes the structure of the outer layer, is not produced. In a microwave oven the products generally do not acquire their desired appearance which is typical of the product involved and the organoleptic properties like smell and flavour, as are achieved when heating in a baking oven.
To resolve that problem special product packagings are known, in which the packaging material itself or a coating applied thereto is heated by the microwave radiation and the product contained therein is heated by delivered radiant heat or convection heat. That way of heating the product is closer to heating in a baking oven than heating by the direct interaction of the product with the microwave radiation so that foodstuffs can also be baked in such packagings and a crust and even surface browning is achieved. The production of special microwave packagings is however complicated and expensive and the known microwave packagings are also not suitable for every form of storage of foodstuffs, for example chilled or deep-frozen storage of doughs.
U.S. Pat. No. 4,283,424 describes a frozen pizza which is said to be suitable specifically for finishing baking or re-heating in a microwave oven, wherein crust formation is achieved by the crust of the pizza including two differently, mutually superposed crust layers. The first crust layer comprises a baked dough material which is typical of a cracker, with a residual moisture content of 5% or less, and the second crust layer arranged directly thereover comprises a baked, bread dough-like type of crust with a residual moisture content of 20 to 40%. The cracker crust is so adapted that it absorbs excess moisture which is produced upon microwave heating and the pizza dough forms a crust.
U.S. Pat. No. 5,194,271 describes a dough composition on the basis of a flour with a high amylose content and which serves as a covering for a dough arranged therebeneath and which upon heating in a microwave oven is intended to form a crispy browned crust.
There is therefore a need for foodstuffs, in particular dough-based products, which can be heated at any time in a microwave oven and in that case a result is achieved similarly to when heating, cooking or baking in a conventional baking oven.